Engine stall anticipation and reaction device

ABSTRACT

In a compressor operating near stall and utilizing the mechanism of variable pitch stator blades to prevent stall, a floating stator blade is used to sense an imminent stall condition. The blade pivots like a weather vane in the airstream flow through the axial flow compressor. The attack angle differential between the variable pitch stator blades and the floating stator blade is sensed and utilized by electrical or fluid pressure means to change the attack angle of the variable pitch stator blades so as to prevent stall.

United States Patent 2,810,512 10/1957 Lippisch 415/23 2,931,168 4/1960Alexander et a1. 60/3927 3,514,212 5/1970 llerbst 4l5/23 FOREIGN PATENTS641,998 8/1950 Great Britain 415/14 Primary Examiner-Samuel FeinbergAttorneys- Edgar J. Brower, Arthur L. Branning and T. 0.

Watson, Jr.

ABSTRACT: In a compressor operating near stall and utilizing themechanism of variable pitch stator blades to prevent stall, a floatingstator blade is used to sense an imminent stall condition. The bladepivots like a weather vane in the airstream flow through the axial flowcompressor. The attack angle differential between the variable pitchstator blades and the floating stator blade is sensed and utilized byelectrical or fluid pressure means to change the attack angle of thevariable pitch stator blades so as to prevent stall.

HIGH PRESSURE FUEL CONOUCTORS PATENTEUnm 19 IHTI 3, 14,253

HIGH PRESSURE FUEL CONDUCTORS FLOATING BLADE F/G. I A

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ATTORNEY ENGINE STALL ANTICIPATION AND REACTION DEVICE STATEMENT OFGOVERNMENT INTEREST The invention described herein may be manufacturedand used by or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefor.

BACKGROUND OF THE INVENTION The present invention is concerned with theanticipation of stall conditions in a jet engine compressor and theprevention of a stall condition which would seriously impair theperformance of the engine. The invention is more particularly concernedwith the use of a freely floating stator blade as a sensor foranticipating imminent stall conditions in the compressor section of ajet engine and with controlling the variable geometry of an axial flowcompressor so as to prevent a stall condition such as would seriouslyimpair the operation of the jet engine. The problem of stall in an axialflow compres sor is not a new one in the art and there have been manymethods devised to sense and obviate the problem. The majority of thedevices designed for obviating stall conditions in an axial flowcompressor utilize sensors which are sensitive to either temperature,pressure or speed of the compressor. These variables at best are onlyindirect indicators of a stall condition. Another approach to theproblem consists of sensing the sonic frequencies produced by animminent stall condition and controlling the geometry of the compressorin response to the occurrence of these sounds. The problem ofeffectively anticipating stall by monitoring the conditions in the airflow through the compressor still remains.

SUMMARY OF THE INVENTION This invention suggests the use of a floatingstator blade to detect an imminent stall condition. The floating statorblade would be located among the variable stator blades. Theinstallation of the floating stator blade is such that it weather cocksand positions itself with respect to the airflow past it. As a stallcondition begins to form within the compressor, the floating blade,because it is essentially unrestrained, starts to move (weather cock) asthe airflow changes its direction. The angle of attack of the variablestator blades do not change because these blades are held stationary bythe variable geometry drive actuators, but the angle of attack of thefloating blade remains more or less constant since it is free to'move inresponse to the condition associated with the change in airflow throughthe compressor. If the relationship between the variable stator bladesand the floating blade is derived, by mechanical means, pressure changesor electrical means, a means of sensing an imminent stall condition isavailable. Besides using this blade sensor to actuate the variablestator blades in a manner so as to prevent stall, it could also be usedto actuate other devices such as a fuel feed control device to cut backfuel flow and assist in the overall program to eliminate complete stallin jet engines.

OBJECTS OF THE INVENTION It is an object of the present invention toprovide a stall anticipation and prevention system for jet enginecompressors operating near stall conditions which is uncomplicated butstill effectively sensitive.

Another object of the present invention is to provide an uncomplicatedstall anticipation and prevention system for jet engine axial flowcompressors operating near stall conditions which permits compressors tooperate closer to the stall line without creating adverse engineoperation than was before possible with such uncomplicated equipment.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING movement into the physical forcerequired to move the variable stator vanes; and

FIG. 2 illustrates another embodiment of the invention in schematic formin which the free-floating blade is spring loaded to follow the normalstator blade positions but allowed freedom, within the limits of theapplied loads, to move in response to airflow direction changes.

1 DESCRIPTION OF THE PREFERRED EMBODIMENTS With more particularreference to FIG. I of the drawing which illustrates a preferredembodiment of the invention functioning in relation with the fuel feedand control system 22 of a standard jet engine, the variable stator vaneactuating mechanism of standard and well-known jet engines is actuatedin response to the floating blade means. Free floating blade I islocated among the variable stator blades of a compressor and iseffectively damped against oscillation by damping means 21. Upon achange in the direction of airflow through the axial flow compressor,the floating blade I, pivots on its axis to follow the direction ofchange in the airflow. The helical screw follower 2 attached to theshaft of the floating blade rotates in the same direction as the blade.Assuming for illustration's sake that the rotation of blade I is in acounterclockwise direction, as illustrated by the arrow, the follower 3of lever 4 rides in the grooves of helical screw 2 as it rotates. Thedirection of rotation tends to cause follower 3 to ride up causing end 5to move downwards as indicated by the arrow. This downward motion of end5 causes spring 6 to expand placing a force on lever 7 which pivots atthe point indicated. Lever 7 in turn places a force on piston rod 8, ina direction indicated by the arrow, to move piston 9 to the right, asindicated by the arrow, so as to lie under cylinder vent F, while stilllying over low-pressure outlet F Because of the spindle typeconstruction of piston 9, cylinder vent F, discharges its high-pressurefuel around the smaller circumference of piston 9 into outlet F: andback into the fuel feed and control system of the jet engine. Thiscauses a decrease in pressure on one side of piston 15 of the statorvane actuator cylinder 16. Piston 15 will move in the low-pressuredirection, as indicated by the arrow, causing linkage shaft 10 attachedto piston 15 to move in that direction also. The movement of linkageshaft 10 will cause feedback cable II to move in the direction indicatedby the arrow. The variable stator blade mechanism, including linkage l2and linkage 13 will move as indicated and variable stator vane 14 willmove to follow the: direction of movement of floating blade 1. Becauseof the movement of feedback cable 11, an expanding force is exerted onspring I7 in the direction indicated by the arrow, which places a forceon piston rod 18 connecting spring 117 and piston 9, tending to bringpiston 9 back to its null position as shown. When the piston 9 is inthis null position, high-pressure fluid conductors I9 and 20 havingoutlets F and F 1 are at equal pressure and piston 15 will remain in theposition it took on the last movement of variable stator blade 14.Piston inlets F 4 and F are the high-pressure boost inlets coming fromthe fuel feed and control system of the jet engine. Piston outlet F isthe low-pressure outlet going to the fuel feed and control system of theengine. There is a substantial pressure differential between the twohigh-pressure fuel inlets F, and IF, and the low-pressure fuel outlet FAs can be readily seen, if the free-floating blade I tended to move in aclockwise direction the helical screw follower 2 would follow thatmovement and so would the other mechanical elements of the system. Thedirection of system movement would be opposite to the directionsindicated by the arrows in FIG. I.

From the foregoing explanation of the embodiment shown in FIG. I it isclear that free floating blade 1 moves in response to a stall conditionand the variable stator blade 14 follows the direction of movement offloating blade 1 so as to prevent stall in the axial flow compressor.

Stall conditions generally being of the intermittent type, free-floatingblade 1 will follow the changing airflow which should soon return tonormal again causing the control equipment to actuate in a manner so asto reposition variable stator blade 14 in the newly desired positiontaken by free-floating blade 1. It should be pointed out that thissystem is not designed to allow a compressor to operate in a continuousstall condition but rather allows the compressor to accommodate anintermittent stall condition without feeling any deleterious effectstherefrom and thereafter go back to operating on' its designedperformance curve.

Referring now to FIG. 2 which shows another embodiment of the invention,the floating stator blade 28 is mounted in the variable stator bladesection of a compressor housing by means of bearings and shaftsconnecting the floating blade to rotating shaft 23 which by means ofbevel gear drive shafts 24 and 26 of the variable stator blades and thefree-floating blade, respectively. The floating blade 28 will line upwith the variable stator blade 25 and follow, due to the tension exertedby spring 27 caused by the rotating force exerted by shaft 23, theposition of variable stator blade 25. As a stall condition begins tooccur in the axial flow compressor, the free-floating blade 28 will tendto change its direction in accordance with the direction of flow in thecompressor. The variable stator blade 25, however, is held stationary bythe rotating shaft 23 its beveled gears and shaft 24. Because of therotation of freefloating blade 28 and the stationary condition of statorblade 25, the spring 27 is placed in a compressive or expansive state.This state is sensed by means of strain gauges placed on spring 27 whichindicate by a small electrical signal of either a negative or positivepolarity whether the spring has been placed in compression or expansion.These signals are carried to an amplifier 31 by cables 29 and 30. Theamplifier 31 amplifies these signals and feeds them to the variablestator actuator mechanism 32 which can be any well-known mechanism suchas a motor drive which will rotate shaft 23 in the appropriate directionas indicated by the magnitude and direction of signals produced by thestrain gauges. The variable stator blade 25 is thus caused to line upwith the position assumed by free-floating blade 28 thereby removing thetension or compression of spring 27. The strain gauges therefore willproduce no output and no further changes in the geometry of the statorblades will occur until another change in the airflow direction occursin the axial flow compressor which will again rotate free-floating blade27 and again cause the control equipment to go through its functionalrelationships. As can be seen, floating blade 28 can rotate in either aclockwise or counterclockwise direction in response to any directionchange in the airflow giving an effective response to an imminent stallcondition. It is contemplated that variable stator actuating mechanism32, besides actuating shaft 23, to rotate variable stator blades 25,could also be used to actuate other devices such as the fuel feedcontrol of a jet engine to cut back fuel flow and thereby assist in theoverall program to eliminate complete stall conditions in the jetengine. The strain gauges used are standard gauges well known-in the artand adapted to produce a positive or negative output depending on theforce applied to them. The strain gauge amplifier 31 is well known inthe art and the variable stator actuating mechanism can be any of anumber of motor means responsive to the amplifier output to drive therotating shaft 23 in either direction, as required. The output 33 ofvariable stator actuator mechanism 32 is a force which can actmechanically to increase ordecrease jet fuel flow and further aid install prevention. Such a method is well known in the art and is not seenas needing further discussion.

While several preferred embodiments of the present invention have beenillustrated and described it will be obvious to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. An apparatus for anticipating and preventing stall in axial flow jetengine compressors which have one or more stages and utilize variablestator blades to control operating characteristics of the compressorhaving a compressor housing adapted for rotatably mounting said variablestator blades thereon comprising at least one floating stator blade pervariable stator blade stage rotatably mounted among said variable statorblades so as to allow said floating stator blade to align itself withairstream flow in said compressor;

a follower means responsive to rotational movement of said floatingstator blade;

a damping means restraining said floating stator blade from freelyrotating in response to minute direction changes in said airstream flow;

a control means responsive to actuation by said follower means; and

adjustment means responsive to said control means to actuate saidvariable stator blades to follow the movement of said floating statorblade whereby a complete stall condition is averted.

2. The stall anticipating and preventing apparatus as recited in claim 1wherein said follower means comprises a shaft rigidly attached to saidfloating stator blade so as to rotate with said floating blade; and

rotary motion to linear motion conversion means responsive to rotationof said shaft to actuate said control means.

3. The stall anticipating and preventing apparatus as recited in claim 2wherein said control means comprises a fluid flow directing meansresponsive to a force exerted by said motion conversion means to directhigh-pressure fluid flow;

high-pressure fluid conductors for transmitting said directed fluidflow;

a fluid pressure activated piston responsive to fluid flow transmittedby said conductors to actuate said adjustment means; and

feedback means responsive to movement of said piston to apply a forceopposite in direction to the force applied by said motion conversionmeans being of sufficient strength to reposition said fluid flowdirecting means to a null position.

4. The stall anticipating and preventing apparatus as recited in claim 1further comprising a fuel feed means responsive to said control meansfor decreasing volume of fuel flow to the jet engine.

5. An apparatus for anticipating and preventing stall in axial flow jetengine compressors which have one or more stages and utilize variablestator blades to control operating characteristics of the compressorhaving a compressor housing adapted for rotatably mounting said variablestator blades thereon comprising at least one floating stator blade pervariable stator blade stage rotatably mounted among said variable statorblades so as to allow said floating stator blade to align itself withairstream flow in said compressor;

a follower means responsive to rotational movement of said floatingstator blade; said follower means comprising a shaft rigidly attached tosaid floating stator blade so as to rotate with said floating blade, anda resilient means rigidly attached and deformably responsive to rotationof said shaft;

a control means responsive to actuation by said follower means; and

adjustment means responsive to said control means to actuate saidvariable stator blades to follow the movement of said floating statorblade whereby a complete stall condition is averted.

6. The stall anticipating and preventing apparatus as recited in claim 5wherein said control means comprises a transducer responsive todeformation of said resilient means;

a transducer amplifier; and

bevel gear combinations transmitting rotary motion from said rotatingshaft to the rotatable shafis of said variable stator blades and saidfloating stator blade.

8. The stall anticipating and preventing apparatus as recited in claim 5further comprising a fuel feed means responsive to said control meansfor decreasing volume of fuel flow to the jet engine.

1. An apparatus for anticipating and preventing stall in axial flow jetengine compressors which have one or more stages and utilize variablestator blades to control operating characteristics of the compressorhaving a compressor housing adapted for rotatably mounting said variablestator blades thereon comprising at least one floating stator blade pervariable stator blade stage rotatably mounted among said variable statorblades so as to allow said floating stator blade to align itself withairstream flow in said compressor; a follower means responsive torotational movement of said floating stator blade; a damping meansrestraining said floating stator blade from freely rotating in responseto minute direction changes in said airstream flow; a control meansresponsive to actuation by said follower means; and adjustment meansresponsive to said control means to actuate said variable stator bladesto follow the movement of said floating stator blade whereby a completestall condition is averted.
 2. The stall anticipating and preventingapparatus as recited in claim 1 wherein said follower means comprises ashaft rigidly attached to said floating stator blade so as to rotatewith said floating blade; and rotary motion to linear motion conversionmeans responsive to rotation of said shaft to actuate said controlmeans.
 3. The stall anticipating and preventing apparatus as recited inclaim 2 wherein said control means comprises a fluid flow directingmeans responsive to a force exerted by said motion conversion means todirect high-pressure fluid flow; high-pressure fluid conductors fortransmitting said directed fluid flow; a fluid pressure activated pistonresponsive to fluid flow transmitted by said conductors to actuate saidadjustment means; and feedback means responsive to movement of saidpiston to apply a force opposite in direction to the force applied bysaid motion conversion means being of sufficient strength to repositionsaid fluid flow directing means to a null position.
 4. The stallanticipating and preventing apparatus as recited in claim 1 furthercomprising a fuel feed means responsive to said control means fordecreasing volume of fuel flow to the jet engine.
 5. An apparatus foranticipating and preventing stall in axial flow jet engine compressorswhich have one or more stages and utilize variable stator blades tocontrol operating characteristics of the compressor having a compressorhousing adapted for rotatably mounting said variable stator bladesthereon comprising at least one floating stator blade per variablestator blade stage rotatably mounted among said variable stator bladesso as to allow said floating stator blade to align itself with airstreamflow in said compressor; a follower means responsive to rotationalmovement of said floating stator blade; said follower means comprising ashaft rigidly attached to said floating stator blade so as to rotatewith said floating blade, and a resilient means rigidly attached anddeformably responsive to rotation of said shaft; a control meansresponsive to actuation by said follower means; and adjustment meansresponsive to said control means to actuate said variable stator bladesto follow the movement of said floating stator blade whereby a completestall condition is averted.
 6. The stall anticipating and preventingapparatus as recited in claim 5 wherein said control means comprises atransducer responsive to deformation of said resilient means; atransducer amplifier; and variable stator actuating means responsive tosaid transducer amplifier to rotatably actuate said adjustment means. 7.The stall anticipating and preventing apparatus as recited in claim 6wherein said adjustment means comprises a rotating shaft responsive tosaid variable stator actuating means; rotatable shafts rigidly attachedto said variable stator blades so as to rotate with said variable statorblades; and bevel gear combinations transmitting rotary motion from saidrotating shaft to the rotatable shafts of said variable stator bladesand said floating stator blade.
 8. The stall anticipating and preventingapparatus as recited in claim 5 further comprising a fuel feed meansresponsive to said control means for decreasing volume of fuel flow tothe jet engine.